I. Field of the application
The present invention relates to metallurgy, and more particularly to a method and apparatus for introducing powdered reagents into molten metals.
The invention is adaptable for application in the production of cast iron, steel and nonferrous metals for accomplishing treatment, desulphurization, overheating and alloying thereof, as well as for the production of high-grade and high-strength cast irons with globular graphite directly in a melting apparatus, metallurgical vessel or in a ladle.
An ever growing production of alloying and special steels by the oxygen-converter process, widely practiced in industrially developed countries, requires an ever greater amount of refined cast irons free from harmful inclusions such as sulphur and phosphorus. This, in turn, stimulates the development of technological processes and equipment for the production of refined molten irons. These technological processes are needed to reduce the production cost of alloying and special steels; to minimize the consumption of powdered reagents and to enhance their efficiencies; to render the metal treating process effective and easily adaptable for mechanized and automatic performance.
There is widely used in modern practice a method for the treatment or desulphurization of liquid blast-furnace cast iron, according to which molten iron is treated with powder-like or lump reagents such as calcium carbide, lime and magnesium.
The above-mentioned method for treating liquid cast iron is not free from disadvantages, such as low efficiency of the reagents being used and high production cost of metal. In addition, the prior-art methods are inefficient by reason of the operating process being discontinuous.
There is also known a method of treating molten iron, which is effected by way of introducing fluidized powders into open-type ladles.
U.S. Pat. No. 2,803,533 describes a method of injecting fluidized powders for metallurgical treatment, according to which fluidized powders, for example, calcium carbide, are introduced through an injection tube into a molten metal to thereby accomplish its desulphurization.
According to another prior-art method for introducing various additives into a molten metal, a metallic tuyere is immersed into a molten metal contained in a ladle, through which various powdered reagents are introduced into the molten metal. As the molten metal is poured into the ladle, the end portion of the tuyere is melted down and the tuyere is gradually lowered.
The both methods described above are disadvantageous in that the tuyere is introduced into the molten metal through the surface layer thereof, which results in undesirable waste of metal due to metal splashing. In addition, these methods require substantial consumption of powdered reagents.
It is known to utilize an apparatus for carrying out desulphurization of liquid iron. This apparatus operates as follows. A powdered reagent, such as lime or calcium carbide, is fed onto the surface of liquid metal contained in a cast-iron ladel. A T-type mixer is introduced from above into the molten metal wherein it rotates about its axis while being driven from a motor through a reducer.
The molten metal starts to circulate and then comes into intimate contact with the powder reagent, whereby the efficiency of metal desulphurization is enhanced.
The disadvantage of the above-described apparatus lies in that the mixer is complicated and cumbersome in construction. The loss of metal due to its adherence to the mixer surface is likewise considerable. Furthermore, the apparatus is utilized inefficienctly due to the fact that only half or two-thirds of the ladle volume is filled with molten metal, hence low throughput capacity of the ladle.
There is also known an apparatus for introducing powdered reagents into molten metal (cf. USSR Inventor's Certificate No. 293,355 cl. C 21c). The apparatus of this invention is operated so that powdered reagents are fed from a hopper into a molten metal through a tuyere immersed in metal for a depth of 1.4 to 1.5 times the entire depth of the metal layer.
The tuyere is made up of concentrically positioned steel tubes 20 to 110 mm in diameter. Each of said steel tubes is enclosed in a chamotte cylinder with refractory coating. The end portion of the tuyere is fitted with a refractory headpiece. The tuyere is immersed in the molten metal contained in a ladle by means of a rod which is fixed on a slide carriage. The rod is lifted by means of a hoist and goes down by gravity. To minimize metal losses due to spattering, only two-thirds of the ladle volume is filled with molten metal.
The apparatus described above suffers from several disadvantages, i.e. the tuyere is complicated in construction and has a short service life; the hoisting device for lifting and displacing the tuyere is cumbersome; it is necessary to introduce a maximum amount of powdered reagents in a short period of time; the efficiency of the powdered reagent is very low, just as the throughput capacity of ladles.
There is known a method of blowing powdered reagents into a molten metal, which consists in that a powdered reagent is fed in a stream of gas into the lower layers of molten metal through a tuyere. After a given amount of the powder reagent required for desulphurization has been fed, its feeding is discontinued and the blowing system is used for the air or oxygen supply.
This method has a disadvantage which resides in that the molten metal is flowed under pressure into the tuyere, as the blowing operation is discontinued, wherein it solidifies thus making the latter inoperative.
To avoid this deficiency, a flow of gas should be fed into the metal container, which, however, is undesirable for this will cause a change in the chemical composition of the metal and premature wear-out of the tuyere.
In addition, the above method is not adapted for the application where vessels, such as open-type ladles, are used.
There is also known an apparatus for introducing powdered reagents into molten metals, which comprises a connection pipe built into the refractory lining of a container and provided with a changeable plug and a slidable tube positioned therein and accommodating a changeable plug and a rod. The lateral side of the tube is formed with a hole equal in diameter to the inlet opening of the connection pipe. The slidable tube is welded to the connection pipe of the tube, thereby providing for the supply of powdered reagents.
This type of apparatus is only suitable for use where only stationary mounted containers are employed, and unsuitable for use with movable or non-stationary ones.
In addition, the pipeline system of the apparatus is often-times clogged with powdered reagents.